Gap fill methods for dram

ABSTRACT

Methods of forming memory devices are described. Some embodiments of the disclosure utilize a low temperature anneal process to reduce bottom voids and seams in low melting point, low resistance metal buried word lines. Some embodiments of the disclosure utilize a high density dielectric cap during a high temperature anneal process to reduce bottom voids in buried word lines.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.16/804,226, filed Feb. 28, 2020, which claims priority to U.S.Provisional Application No. 62/813,211, filed Mar. 4, 2019, and U.S.Provisional Application No. 62/832,572, filed Apr. 11, 2019, the entiredisclosures of which are hereby incorporated by reference herein.

TECHNICAL FIELD

Embodiments of the present disclosure pertain to the field of electronicdevices and electronic device manufacturing. More particularly, someembodiments of the disclosure provide dynamic random-access memory cellswith buried word lines comprising low melting point metals and/or havingreduced resistance.

BACKGROUND

Electronic devices, such as personal computers, workstations, computerservers, mainframes and other computer related equipment such asprinters, scanners and hard disk drives use memory devices that providesubstantial data storage capability, while incurring low powerconsumption. There are two major types of random-access memory cells,dynamic and static, which are well-suite for use in electronic devices.Dynamic random-access memories (DRAMs) can be programmed to store avoltage which represents one of two binary values, but require periodicreprogramming or “refreshing” to maintain this voltage for more thanvery short periods of time. Static random-access memories (SRAM) are sonamed because they do not require periodic refreshing.

DRAM memory circuits are manufactured by replicating millions ofidentical circuit elements, known as DRAM cells, on a singlesemiconductor wafer. Each DRAM cell is an addressable location that canstore one bit (binary digit) of data. In its most common form, a DRAMcell consists of two circuit components: a field effect transistor (FET)and a capacitor.

The manufacturing of a DRAM cell includes the fabrication of atransistor, a capacitor, and three contacts: one each to the bit line,the word line, and the reference voltage. DRAM manufacturing is a highlycompetitive business. There is continuous pressure to decrease the sizeof individual cells and to increase memory cell density to allow morememory to be squeezed onto a single memory chip, especially fordensities greater than 256 Megabits. Limitations on cell size reductioninclude the passage of both active and passive word lines through thecell, the size of the cell capacitor, and the compatibility of arraydevices with non-array devices.

In manufacturing, DRAM word lines often need to be able to endure severethermal conditions which are necessary for later processing steps of thecircuits. These severe thermal conditions can lead the metal contacts ofthe word line to delaminate and form bottom voids where the metal gapfill pulls-up from the bottom surface to form a void in the word linetrench.

Therefore, there is a need for gap fill methods of forming lowresistance buried word lines in DRAM cells able to withstand furtherprocessing conditions without forming bottom voids.

Further, the detection of the bottom voids during processing can bechallenging. The defects associated with bottom voids are often notapparent until the device has been fully formed. The full process flowfor forming a memory device can take approximately 6-8 weeks.Accordingly, device defects may not be apparent until 6-8 weeks afterthe word line is formed.

DRAM devices are often manufactured using high volume manufacturing(HVM) techniques. HVM techniques seek to manufacture many devicessimultaneously. Therefore, there is a need for methods to evaluate wordlines without having to wait for the full device formation process.

SUMMARY

One or more embodiments of the disclosure are directed to a method offorming a memory device. The method comprises providing a substratehaving plurality of trenches thereon. Each trench has a trench depth. Aconformal gate oxide layer is deposited on the substrate. A thickness ofa first metal layer is formed on the conformal gate oxide layer. Thethickness is less than or equal to 90% of the trench depth. A lowtemperature anneal of the substrate is performed. A thickness of asecond metal layer is formed on the first metal layer. The thickness ofthe second metal layer at least fills the trench. The second metal layeris recessed to a predetermined depth to form a recessed metal layer.

Additional embodiments of the disclosure are directed to methods offorming a memory device. The methods comprise providing a substratehaving plurality of trenches thereon. Each trench has a trench depth. Aconformal gate oxide layer is deposited on the substrate. A thickness ofa metal layer is formed on the conformal gate oxide layer. The thicknessat least fills the trench. A low temperature anneal of the substrate isperformed. The metal layer is recessed to a predetermined depth to forma recessed metal layer. A high density dielectric layer is deposited onthe recessed metal layer. A high temperature anneal of the substrate isperformed. The high density dielectric layer is removed.

Further embodiments of the disclosure are directed to methods of forminga memory device. The methods comprise providing a substrate havingplurality of trenches thereon. Each trench has a trench depth. Aconformal gate oxide layer is deposited on the substrate. A thickness ofa metal layer is formed on the conformal gate oxide layer. The thicknessis less than or equal to 90% of the trench depth. A low temperatureanneal of the substrate is performed. An additional thickness of themetal layer is formed. The total thickness of the metal layer at leastfills the trench. The metal layer is recessed to a predetermined depthto form a recessed metal layer. A high density dielectric layer isdeposited on the recessed metal layer. A high temperature anneal of thesubstrate is performed. The high density dielectric layer is removed.

BRIEF DESCRIPTION OF THE DRAWING

So that the manner in which the above recited features of the presentdisclosure can be understood in detail, a more particular description ofthe disclosure, briefly summarized above, may be had by reference toembodiments, some of which are illustrated in the appended drawings. Itis to be noted, however, that the appended drawings illustrate onlytypical embodiments of this disclosure and are therefore not to beconsidered limiting of its scope, for the disclosure may admit to otherequally effective embodiments. The embodiments as described herein areillustrated by way of example and not limitation in the figures of theaccompanying drawings in which like references indicate similarelements.

FIG. 1 illustrates a circuit diagram of a DRAM cell block in accordancewith the prior art;

FIG. 2 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 3 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 4 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 5 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 6 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 7 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 8 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 9 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 10 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 11 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 12 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 13 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 14 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 15 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 16 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure;

FIG. 17 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure; and

FIG. 18 illustrates a cross-section view of a device according to one ormore embodiments of the disclosure.

DETAILED DESCRIPTION

Before describing several exemplary embodiments of the disclosure, it isto be understood that the disclosure is not limited to the details ofconstruction or process steps set forth in the following description.The disclosure is capable of other embodiments and of being practiced orbeing carried out in various ways.

As used in this specification and the appended claims, the terms“precursor”, “reactant”, “reactive gas” and the like are usedinterchangeably to refer to any gaseous species that can react with thesubstrate surface.

As used herein, the term “dynamic access random memory” or “DRAM” refersto a memory cell that stores a datum bit by storing a packet of charge(or not, for a zero) on a capacitor; the charge is gated onto thecapacitor via an access transistor, and sensed by turning on the sametransistor and looking at the voltage perturbation created by dumpingthe charge packet on the interconnect line on the transistor output.Thus, a single DRAM cell is made of one transistor and one capacitor.The DRAM device, as illustrated in FIG. 1, is formed of an array of DRAMcells. The rows on access transistors are linked by word lines 52 a, 52b, and the transistor inputs/outputs are linked by bitlines 54 a, 54 b,54 c. Historically, DRAM capacitors have evolved from planarpolysilicon-oxide-substrate plate capacitors to 3-D structures whichhave diverged into “stack” capacitors with both plates above thesubstrate), and “trench” capacitors using an etched cavity in thesubstrate as the common plate.

Traditionally, DRAM cells have recessed high work-function metalstructures in buried word line structure. In a DRAM device, a bitline isformed in a metal level situated above the substrate, while the wordline is formed at the polysilicon gate level at the surface of thesubstrate. In a buried word line (bWL) device, a word line is buriedbelow the surface of a semiconductor substrate using a metal as a gateelectrode.

The selection of metal to be used as a gate electrode can greatly impactthe performance of the device. Without being bound by theory, it isbelieved that the use of low melting point metals with low resistanceadvantageously provides bWL DRAM with reduced resistance. However, whenexposed to the thermal process requirements used in manufacturing bWLDRAM, these materials are often found to display bottom voids where thematerial at the bottom of a trench has pulled away from the bottomsurface. These bottom voids can impact final array resistance and causereliability issues.

Exemplary embodiments are described herein with reference tocross-sectional illustrations that are schematic illustrations ofexemplary substrates. As such, variations from the shapes of theillustrations as a result, for example, of manufacturing techniquesand/or tolerances, are to be expected. Thus, the illustrated embodimentsshould not be construed as limited to the particular shapes of regionsillustrated herein but may be understood to include deviations in shapesthat result, for example, from manufacturing. For example, an implantedregion illustrated as a rectangle may, typically, have rounded or curvedfeatures and/or a gradient of implant concentration at its edges ratherthan a binary change from implanted to non-implanted region. Likewise, aburied region formed by implantation may result in some implantation inthe region between the buried region and the surface through which theimplantation takes place. Thus, the regions illustrated in the figuresare schematic in nature and their shapes are not intended to illustratethe actual shape of a region of a device and are not intended to limitthe scope of disclosure.

Some embodiments of this disclosure advantageously form memory deviceswith high quality gap fill with a low melting point, low resistance andreduced bottom voids. FIGS. 2 through 10 are cross-sectional viewsillustrating a memory device 100 in various stages of processingaccording to one or more embodiments which utilize a low temperatureanneal process.

Referring to FIG. 2, a substrate 102 is provided having a plurality oftrenches 104 therein. The trenches 104 form a recessed channel. Thetrenches have a bottom 106 and sidewall 108. The plurality of trenches104 may be formed so as to have a width within a range of about 10 toabout 100 nm, including, but not limited to a range of about 10 nm toabout 80 nm, about 10 nm to about 70 nm, about 10 nm to about 60 nm,about 10 nm to about 50 nm, or about 10 nm to about 40 nm. As will berecognized by one of skill in the art, the width of the plurality oftrenches 104 is defined by a distance W1 from one sidewall 108 toanother sidewall 108. The plurality of trenches 104 may be formed so asto have a depth within a range of about 120 nm to about 250 nm,including, but not limited to a range of about 120 nm to about 150 nm,about 150 nm to about 200 nm, about 200 nm to about 250 nm, about 120 nmto about 200 nm, or about 150 nm to about 250 nm. As will be recognizedby one of skill in the art, the depth of the plurality of trenches 104is defined by the distance D1 from the substrate surface 103 to thebottom 106 of the plurality of trenches 104.

A “substrate” as used herein, refers to any substrate or materialsurface formed on a substrate upon which film processing is performedduring a fabrication process. For example, a substrate surface on whichprocessing can be performed include materials such as silicon, siliconoxide, strained silicon, silicon on insulator (SOI), carbon dopedsilicon oxides, amorphous silicon, doped silicon, germanium, galliumarsenide, glass, sapphire, and any other materials such as metals, metalnitrides, metal alloys, and other conductive materials, depending on theapplication. Substrates include, without limitation, semiconductorwafers. Substrates may be exposed to a pretreatment process to polish,etch, reduce, oxidize, hydroxylate, anneal and/or bake the substratesurface. In addition to film processing directly on the surface of thesubstrate itself, in the present disclosure, any of the film processingsteps disclosed may also be performed on an under-layer formed on thesubstrate as disclosed in more detail below, and the term “substratesurface” is intended to include such under-layer as the contextindicates. Thus for example, where a film/layer or partial film/layerhas been deposited onto a substrate surface, the exposed surface of thenewly deposited film/layer becomes the substrate surface.

In order to form the plurality of trenches 104, a buffer insulatinglayer (e.g. a silicon oxide layer, not shown) may be formed on thesubstrate surface 103, and/or a hard mask layer (e.g. a nitride layer,not illustrated) may be formed. Such technique is well known to thoseskilled and the art, and, thus, is not illustrated.

With reference to FIG. 3, a gate oxide layer 110 is conformallydeposited on the substrate 102, on the substrate surface 103 and alongthe sidewall 108 and bottom 106 of the plurality of trenches 104. In oneor more embodiments, the gate oxide layer 110 comprises one or more ofsilicon oxynitride (SiON), silicon oxide, or a high-K dielectricmaterial. While the term “silicon oxide” may be used to describe thegate oxide layer 110, the skilled artisan will recognize that thedisclosure is not restricted to a particular stoichiometry. For example,the terms “silicon oxide” and “silicon dioxide” may both be used todescribe a material having silicon and oxygen atoms in any suitablestoichiometric ratio. The same is true for the other materials listed inthis disclosure, e.g. silicon nitride, silicon oxynitride, tungstenoxide, zirconium oxide, aluminum oxide, hafnium oxide, and the like.

In one or more embodiments, the term “high-K dielectric” refers to amaterial with a high dielectric constant (as compared to, e.g. silicondioxide). In one or more embodiments, the high-K dielectric material isselected from one or more of hafnium oxide (HfO2), zirconium oxide(ZrO2), vanadium oxide (VO2), titanium oxide (TiO2), tin oxide (SnO2),aluminum oxide (Al2O3), zinc oxide (ZnO), hafnium silicon oxide (HfSiO),or zirconium silicon oxide (ZrSiO).

In one or more embodiments, the gate oxide layer 110 has a thickness ina range of about 1 nm to about 7 nm, including about 1 nm, about 2 nm,about 3 nm, about 4 nm, about 5 nm, about 6 nm, or about 7 nm.

With reference to FIGS. 4 and 5, a first metal layer 113 is formed onthe gate oxide layer 110. In one or more embodiments, the first metallayer 113 is formed by depositing a work-function metal layer 112 (seeFIG. 4) on the gate oxide layer 110, followed by depositing a metallayer 114 (see FIG. 5) on the work-function metal layer 112.

As used herein, the term “work-function” refers to the bulk chemicalpotential of a material (e.g. metal) relative to the vacuum level. Inone or more embodiments, the work-function metal layer has a workfunction greater than or equal to 4.3 eV. In some embodiments, thework-function metal layer has a work function greater than or equal to4.5 eV. In other embodiments, the work-function metal layer has awork-function greater than or equal to 4.3 eV, including greater than orequal to 4.4 eV, greater than or equal to 4.5 eV, greater than or equalto 4.6, greater than or equal to 4.7 eV, greater than or equal to 4.8eV, greater than or equal to 4.9 eV, greater than or equal to 5.0 eV,greater than or equal to 5.1 eV, or greater than or equal to 5.2 eV.

In one or more embodiments, the work-function metal layer comprises ametal nitride. In one more embodiments, the work-function metal layercomprises one or more of titanium nitride (TiN), tungsten nitride (WN),tantalum nitride (TaN), molybdenum nitride (MoN), TaN/TiN, or WN/TiN. Inone more embodiments, the work-function metal layer is selected from thegroup consisting of titanium nitride (TiN), tungsten nitride (WN),tantalum nitride (TaN), molybdenum nitride (MoN), TaN/TiN, WN/TiN, andcombinations thereof. In one or more embodiments, the work-functionmetal layer comprises titanium nitride. In one or more embodiments, thework-function metal layer may also be referred to the high/midwork-function metal layer.

In one or more embodiments, the work-function metal layer 112 has athickness in a range of about 1 nm to about 5 nm, including about 1 nm,about 2 nm, about 3 nm, about 4 nm, or about 5 nm.

The metal layer 114 is deposited using any one of a number of methodsknown to one of skill in the art, including, but not limited to,chemical vapor deposition, physical vapor deposition, or atomic layerdeposition.

“Atomic layer deposition” or “cyclical deposition” as used herein refersto the sequential exposure of two or more reactive compounds to deposita layer of material on a substrate surface. The substrate, or portion ofthe substrate, is exposed separately to the two or more reactivecompounds which are introduced into a reaction zone of a processingchamber. In a time-domain ALD process, exposure to each reactivecompound is separated by a time delay to allow each compound to adhereand/or react on the substrate surface and then be purged from theprocessing chamber. These reactive compounds are said to be exposed tothe substrate sequentially. In a spatial ALD process, different portionsof the substrate surface, or material on the substrate surface, areexposed simultaneously to the two or more reactive compounds so that anygiven point on the substrate is substantially not exposed to more thanone reactive compound simultaneously. As used in this specification andthe appended claims, the term “substantially” used in this respectmeans, as will be understood by those skilled in the art, that there isthe possibility that a small portion of the substrate may be exposed tomultiple reactive gases simultaneously due to diffusion, and that thesimultaneous exposure is unintended.

In one aspect of a time-domain ALD process, a first reactive gas (i.e.,a first precursor or compound A, e.g. aluminum precursor) is pulsed intothe reaction zone followed by a first time delay. Next, a secondprecursor or compound B (e.g. oxidant) is pulsed into the reaction zonefollowed by a second delay. During each time delay, a purge gas, such asargon, is introduced into the processing chamber to purge the reactionzone or otherwise remove any residual reactive compound or reactionby-products from the reaction zone. Alternatively, the purge gas mayflow continuously throughout the deposition process so that only thepurge gas flows during the time delay between pulses of reactivecompounds. The reactive compounds are alternatively pulsed until adesired film or film thickness is formed on the substrate surface. Ineither scenario, the ALD process of pulsing compound A, purge gas,compound B and purge gas is a cycle. A cycle can start with eithercompound A or compound B and continue the respective order of the cycleuntil achieving a film with the predetermined thickness.

In an embodiment of a spatial ALD process, a first reactive gas andsecond reactive gas (e.g., nitrogen gas) are delivered simultaneously tothe reaction zone but are separated by an inert gas curtain and/or avacuum curtain. The substrate is moved relative to the gas deliveryapparatus so that any given point on the substrate is exposed to thefirst reactive gas and the second reactive gas.

As used herein, “chemical vapor deposition” refers to a process in whicha substrate surface is exposed to precursors and/or co-reagentssimultaneous or substantially simultaneously. As used herein,“substantially simultaneously” refers to either co-flow or where thereis overlap for a majority of exposures of the precursors.

Plasma enhanced chemical vapor deposition (PECVD) is widely used todeposit thin films due to cost efficiency and film property versatility.In a PECVD process, for example, a hydrocarbon source, such as agas-phase hydrocarbon or a vapor of a liquid-phase hydrocarbon that havebeen entrained in a carrier gas, is introduced into a PECVD chamber. Aplasma-initiated gas, typically helium, is also introduced into thechamber. Plasma is then initiated in the chamber to create excitedCH-radicals. The excited CH-radicals are chemically bound to the surfaceof a substrate positioned in the chamber, forming the desired filmthereon. Embodiments described herein in reference to a PECVD processcan be carried out using any suitable thin film deposition system. Anyapparatus description described herein is illustrative and should not beconstrued or interpreted as limiting the scope of the embodimentsdescribed herein.

In some embodiments, the metal layer 114 comprises ruthenium. In someembodiments, the metal layer 114 comprising ruthenium is deposited asdescribed below with respect to FIGS. 15-18.

With reference to FIG. 15, in some embodiments, a substrate 102, asshown in FIG. 4, optionally has a ruthenium seed layer 1510 deposited onthe surface of the work-function metal layer 112. Any suitable processmay be used to deposit the ruthenium seed layer 1510. In someembodiments, the ruthenium seed layer 1510 is deposited by aplasma-enhanced atomic layer deposition (PEALD) process. In someembodiments, the substrate 102 is sequentially exposed to a rutheniumprecursor and an ammonia plasma. In some embodiments, the processingpressure is in a range of about 2 torr to about 10 torr.

In some embodiments, as shown, the ruthenium seed layer 1510 isconformal to the surface of the work-function metal layer 112. In someembodiments, the thickness of the ruthenium seed layer 1510 is greaterthan or equal to 0 and less than or equal to about 2 nm.

With reference to FIG. 16, a first quantity 1520 of ruthenium isdeposited on the work-function metal layer 112 or the ruthenium seedlayer 1510. For clarity, in FIG. 16, the gate oxide layer 110 and thework-function metal layer 112 are not shown. The first quantity 1520 ofruthenium is not sufficient to close the top of the trench 104.

The first quantity 1520 of ruthenium may be deposited by any suitableprocess. In some embodiments, the first quantity 1520 of ruthenium isdeposited by an atomic layer deposition process which utilizes aruthenium precursor and an alkyl halide.

After the first quantity 1520 of ruthenium is deposited, the substrateis treated to reduce deposition on the substrate surface 103 and at thetop of the trench 104. In some embodiments, the treatment processcomprises exposing the substrate 102 to hydrogen. In some embodiments,the substrate 102 is exposed to a hydrogen plasma.

Without being bound by theory, it is believed that the hydrogen plasmaof some embodiments prevents deposition on the exposed surfaces. As thedirection of plasma exposure can be controlled, it is possible to treatonly select surfaces. Exposing the substrate 102 to hydrogen plasmaallows for preferential deposition deep within the trench 104 relativeto the substrate surface 103 or at the top of the trench 104. Theprevention of deposition on the substrate surface 103 and at the top ofthe trench 104 reduces the potential for seams and voids within themetal layer 114.

With reference to FIG. 17, a second quantity 1530 of ruthenium isdeposited on the first quantity 1520 of ruthenium. As shown in FIG. 17,after the treatment process described above, the second quantity 1530 ofruthenium is deposited at a greater rate within the trench 104 than onthe substrate surface 103.

With reference to FIG. 18, a low temperature anneal of the substrate isperformed causing the ruthenium seed layer 1510 (if present), the firstquantity 1520 and the second quantity 1530 of ruthenium to reflow intothe trench 104 to form metal layer 114. The low temperature annealconditions are described more fully below.

Without being bound by theory, it is believed that the low temperatureanneal conditions cause the deposited ruthenium to become flowable dueto atomic rearrangements and/or a low melting point. Due to thecapillary effect, ruthenium which is deposited outside of the trench onthe substrate surface 103 is drawn into the trench 104.

In some embodiments, the thickness T1 of the first metal layer 113 iscontrolled. In some embodiments, the thickness T1 of the first metallayer 113 is controlled relative to the depth D1 of the plurality oftrenches 104. In some embodiments, the thickness T1 is less than orequal to about 90%, less than or equal to about 80%, less than or equalto about 75%, less than or equal to about 70%, less than or equal toabout 60%, less than or equal to about 50%, less than or equal to about40%, less than or equal to about 30%, less than or equal to about 25%,or less than or equal to about 20% of the depth D1 of the plurality oftrenches 104.

In some embodiments, a low temperature anneal of the substrate isperformed. While anneal processes are generally well understood in theart, the low anneal process utilized in some embodiments controls thetemperature and duration of exposure. Without being bound by theory, itis believed that the low temperature anneal process allows the firstmetal layer 113 to reflow into the trench, providing a higher qualitygap fill with fewer seams or voids and lower resistance. It is alsobelieved that the reflowing process prevents the later formation ofbottom voids. In some embodiments, after the low temperature annealprocess, the first metal layer 113 contains substantially no seams orvoids. As used in this regard, a material which contains substantiallyno seam or voids has gaps, seams or voids which occupy less than 2%,less than 1% or less than 0.5% of the volume of the stated material.

In some embodiments, the low temperature anneal process is performed ata temperature of less than or equal to about 700° C., less than or equalto about 600° C. or less than or equal to about 500° C. In someembodiments, the low temperature anneal process is performed for aperiod in a range of about 5 minutes to about 20 minutes, about 7minutes to about 15 minutes or about 8 minutes to about 10 minutes. Insome embodiments, the low temperature anneal process is performed for aperiod of less than or equal to about 15 minutes, less than or equal toabout 12 minutes, less than or equal to about 10 minutes, or less thanor equal to about 9 minutes.

With reference to FIG. 6, a thickness T2 of a second metal layer 116 isformed on the metal layer 114. The second metal layer 116 may be formedby any suitable process, including but not limited to those describedherein with respect to metal layer 114. The thickness T2 of the secondmetal layer 116 at least fills the trench 104. Stated differently, thesum of T1 and T2 is greater than or equal to the depth D1 of the trench104. In those embodiments in which the sum of T1 and T2 is in excess ofthe depth D1 of the trench 104, an overburden of the second metal layer116 may be formed on the substrate.

With reference to FIG. 7, the second metal layer 116 is recessed to apredetermined depth D2 from the substrate surface 103. In someembodiments, as shown, the predetermined depth D2 is such that a portionof the second metal layer 116 remains within the trench. In someembodiments, the predetermined depth is such that the second metal layer116 is completely removed from the trench 104.

In some embodiments, the second metal layer 116 is recessed (buried) bychemical mechanical polishing (CMP) and an etch back such that thesecond metal layer 116 and the work-function metal layer 112 do notprotrude beyond the substrate surface 103 (e.g. so that the metal layer114 and, if present, the second metal layer 116 are completely buriedwithin the substrate 102).

In one or more embodiment, a buried word line 115 (i.e. the recessedsecond metal layer 116 and metal layer 114) may be formed. In someembodiments, as illustrated in FIG. 6, the work-function metal layer 112is recessed to the same level as the buried word line 115. A top surface117 of the buried word line 115 and the work-function metal layer 112 isa recess depth or distance D2 from the substrate surface 103 in theplurality of trenches 104.

In one or more embodiments, the metal layer 114 and the second metallayer 116 (i.e. the word line 115) comprise the same metal material. Insome embodiments, the metal layer 114 and second metal layer 116comprise one or more of ruthenium (Ru), molybdenum (Mo) or iridium (Ir).

After formation of the word line 115, processing of the substrate cancontinue to form a memory device. Such processes are known by theskilled artisan. An exemplary process flow for the continued formationof a memory device follows. In some embodiments, the memory deviceformed contains substantially no bottom void. As used in this regard, adevice which contains substantially no bottom void shows no evidence ofbottom peeling or voids between the bottom 106 of the trench 104 and theword line 115.

With reference to FIG. 8, in one or more embodiments, a secondwork-function metal layer 118 is deposited on the substrate 102 on theword line 115. Referring to FIG. 9, the second work-function metal layer118 is then polished using a chemical mechanical polishing (CMP) methodand etched back to expose the substrate surface 103. A top surface 120of the second work-function metal layer 118 is a distance D3 from thesubstrate surface 103 in the plurality of trenches 104. In one or moreembodiments, the second work-function metal layer 118 has a top surface120 within the depth D1 of the trench 104. Accordingly, in one or moreembodiments D3 is less than D1.

In one or more embodiments, the second work-function metal layer 118 hasa thickness T3 in a range of about 10 nm to about 50 nm, including about10 nm, about 15 nm, about 20 nm, about 25 nm, about 30 nm, about 35 nm,about 40 nm, about 45 nm, or about 50 nm.

Referring to FIG. 10, an insulating layer 122 is deposited on the secondmetal layer 116. In one or more embodiments, the insulating layer has atop surface 124 substantially coplanar with the substrate surface 103.

In one or more embodiments, the insulating layer 122 comprises adielectric material. As used herein, the term “dielectric” refers to anelectrical insulator material that can be polarized by an appliedelectric field. In one or more embodiments, the dielectric materialincludes, but is not limited to, oxides, e.g., SiO2, Al2O3, nitrides,e.g., Si3N4. In one or more embodiments, the dielectric materialcomprises silicon nitride (Si3N4). In some embodiments, the insulatinglayer composition is non-stoichiometric relative to the ideal molecularformula. For example, in some embodiments, the dielectric materialincludes, but is not limited to, oxides (e.g., silicon oxide, aluminumoxide), nitrides (e.g., silicon nitride (SiN)), oxycarbides (e.g.silicon oxycarbide (SiOC)), and oxynitrocarbides (e.g. siliconoxycarbonitride (SiNCO)).

Some embodiments of this disclosure advantageously form memory deviceswith high quality gap fill with a low melting point, low resistance andreduced bottom voids. FIGS. 2-4, 11-14 and 8-10 are cross-sectionalviews illustrating a memory device 100 in various stages of processingaccording to one or more embodiments which utilize a high density capduring a high temperature anneal process.

Referring to FIGS. 2-4, a substrate 102 is provided with a plurality oftrenches 104 thereon. The substrate 102 and the trenches 104 are asdescribed above with respect to FIG. 2.

With reference to FIG. 3, a gate oxide layer 110 is conformallydeposited on the substrate 102, on the substrate surface 103 and alongthe sidewall 108 and bottom 106 of the plurality of trenches 104. Theparticulars of the gate oxide layer 110 are as described above withrespect to FIG. 3.

Referring to FIGS. 4 and 11, a first metal layer 113 is formed on thegate oxide layer 110. In one or more embodiments, the first metal layer113 is formed by depositing a work-function metal layer 112 (see FIG. 4)on the gate oxide layer 110, followed by depositing a metal layer 114(see FIG. 11) on the work-function metal layer 112.

Referring to FIG. 11, in some embodiments, the thickness T4 of the metallayer 114 is controlled. In some embodiments, the thickness T4 of themetal layer 114 is controlled relative to the depth D1 of the pluralityof trenches 104. In some embodiments, the thickness T4 of the metallayer 114 at least fills the trench 104. Stated differently, thethickness T4 of the metal layer 114 is greater than or equal to thedepth D1 of the trench 104. In those embodiments in which the thicknessT4 is in excess of the depth D1 of the trench 104, an overburden of themetal layer 114 may be formed on the substrate surface.

In some embodiments, a low temperature anneal of the substrate 102 isperformed. While anneal processes are generally well understood in theart, the low anneal process utilized in some embodiments controls thetemperature and duration of exposure. Without being bound by theory, itis believed that the low temperature anneal process allows the firstmetal layer 113 to reflow into the trench, providing a higher qualitygap fill with fewer seams or voids and lower resistance. It is alsobelieved that the reflowing process prevents the later formation ofbottom voids. In some embodiments, after the low temperature annealprocess, the first metal layer 113 contains substantially no seams orvoids. As used in this regard, a material which contains substantiallyno seam or voids has gaps, seams or voids which occupy less than 2%,less than 1% or less than 0.5% of the volume of the stated material.

In some embodiments, the low temperature anneal process is performed ata temperature of less than or equal to about 700° C., less than or equalto about 600° C. or less than or equal to about 500° C. In someembodiments, the low temperature anneal process is performed for aperiod in a range of about 5 minutes to about 20 minutes, about 7minutes to about 15 minutes or about 8 minutes to about 10 minutes. Insome embodiments, the low temperature anneal process is performed for aperiod of less than or equal to about 15 minutes, less than or equal toabout 12 minutes, less than or equal to about 10 minutes, or less thanor equal to about 9 minutes.

With reference to FIG. 12, the metal layer 114 is recessed to apredetermined depth D2 from the substrate surface 103. In someembodiments, the metal layer 114 is recessed (buried) by chemicalmechanical polishing (CMP) and an etch back such that the metal layer114 and the work-function metal layer 112 do not protrude beyond thesubstrate surface 103 (e.g. so that the metal layer 114 is completelyburied within the substrate 102).

In one or more embodiment, a buried word line 115 (i.e. the recessedmetal layer 114) may be formed. In some embodiments, as illustrated inFIG. 12, the work-function metal layer 112 is recessed to the same levelas the buried word line 115. A top surface 117 of the buried word line115 and the work-function metal layer 112 is a recess depth or distanceD2 from the substrate surface 103 in the plurality of trenches 104. Insome embodiments, the metal layer 114 comprises one or more of ruthenium(Ru) or iridium (Ir).

With reference to FIG. 13, a high density dielectric layer 130 isdeposited on the top surface 117 of the recessed metal layer 114 (i.e.the buried word line 115). The high density dielectric layer may be anysuitable film with a significantly high density. In some embodiments,the high density dielectric layer comprises one or more of SiN or SiCN.In some embodiments, the high density dielectric layer 130 is depositedonly within the trench 104.

The high density dielectric layer 130 may be deposited with a thicknessT5. In some embodiments, as shown, T5 is about D2. In some embodiments,T5 is less than D2 and the trench is not completely filled. In someembodiments, T5 is greater than D2. In some embodiments when T5 isgreater than D2, the high density dielectric material is not depositedon the substrate surface 103. In some embodiments when T5 is greaterthan D2, the high density dielectric layer 130 is deposited on thesubstrate surface 103 outside of the trench 104.

In some embodiments, a high temperature anneal of the substrate 102 isperformed. While anneal processes are generally well understood in theart, the high temperature anneal process utilized in some embodimentscontrols the temperature and duration of exposure. Without being boundby theory, it is believed that the high density cap pushes on the metallayer 114 during the high temperature anneal process to prevent theformation of bottom voids.

In some embodiments, the high temperature anneal process is performed ata temperature of greater than or equal to about 800° C., greater than orequal to about 850° C. or greater than or equal to about 900° C. In someembodiments, the high temperature anneal process is performed at atemperature in a range of about 800° C. to about 900° C.

In some embodiments, the high temperature anneal process is performedfor a period in a range of about 30 seconds to about 1 minute, about 30seconds to about 45 seconds or about 45 seconds to about 1 minute. Insome embodiments, the high temperature anneal process is performed for aperiod of less than or equal to about 2 minutes, less than or equal toabout 1 minute, less than or equal to about 45 seconds, or less than orequal to about 30 seconds.

With reference to FIG. 14, after the high temperature anneal process isperformed, the high density dielectric layer 130 is removed or etchedfrom the substrate. In some embodiments when the high density dielectriclayer 130 comprises SiN, a hot phos etch process may be used to removethe high density dielectric layer 130. After removing the high densitydielectric layer 130, the memory device is similarly formed as in FIG.7, with a buried word line 115 located within a trench 104, and recessedfrom the substrate surface 103 by a distance D2, At this point thesubstrate illustrated in FIG. 14 may be processed through a similarprocess flow as described above with reference to FIGS. 8-10.

Some embodiments of this disclosure advantageously utilize a short loopprocess that enables detection of bottom voids or other issues with theword line 115 without fully forming the memory device. The short loopprocess is able to be performed quicker than the process of fullyforming the memory device. In some embodiments, the short loop processis performed within a period of less than or equal to about 1 week, lessthan or equal to about 3 days or less than or equal to about 1 day.

With reference to FIGS. 13 and 14, after depositing the high densitydielectric layer 130, a short flow high temperature anneal of thesubstrate 102 is performed. In some embodiments, the short flow hightemperature anneal of the substrate differs from the high temperatureanneal conditions described above. In some embodiments, the short flowhigh temperature anneal is performed at a higher temperature and/or fora longer duration than the high temperature anneal conditions describedabove.

Without being bound by theory, it is believed that the highertemperature and/or longer duration of the short flow high temperatureanneal process more accurately simulates that thermal processing of thememory device through the remainder of the formation process. Thissimulation allows for the detection of bottom voids without fullyforming the memory device.

In some embodiments, the short flow high temperature anneal process isperformed at a temperature of greater than or equal to about 850° C.,greater than or equal to about 900° C. or greater than or equal to about950° C. In some embodiments, the short flow high temperature annealprocess is performed at a temperature in a range of about 850° C. toabout 950° C. In some embodiments, the short flow high temperatureanneal process is performed at a temperature of about 900° C.

In some embodiments, the short flow high temperature anneal process isperformed for a period in a range of about 1 minute to about 5 minutes,about 90 seconds to about 4 minutes or about 2 minutes to about 3minutes. In some embodiments, the short flow high temperature annealprocess is performed for a period of about 90 seconds, about 2 minutesor about 3 minutes.

Similar to FIG. 14, after performing the short flow high temperatureanneal process, the high density dielectric layer 130 is removed. Afterthe high density dielectric layer 130 is removed, an evaluation of theword line is performed to detect bottom voids. If bottom voids aredetected, it is believed that the word line would have also exhibitedbottom voids if processed through the remainder of the formationprocess.

In some embodiments, the evaluation is performed by e-beam metrology. Insome embodiments, the e-beam metrology process utilizes a high landingenergy. In some embodiments, the energy of the e-beam metrology processis in a range of about 10 keV to about 25 keV, in a range of about 12keV to about 20 keV, or in a grange of about 15 keV to about 18 keV. Insome embodiments, the energy of the e-beam metrology process is about 12keV, about 15 eV, about 18 keV or about 20 keV.

Some embodiments of this disclosure advantageously form memory deviceswith high quality gap fill with a low melting point, low resistance andreduced bottom voids. FIGS. 2-7, 12-14 and 8-10 are cross-sectionalviews illustrating a memory device 100 in various stages of processingaccording to one or more embodiments which utilize a low temperatureanneal process and a high density cap during a high temperature annealprocess.

In general the process described herein should be understood by oneskilled in the art as a combination of the two previously disclosedmethods.

Referring to FIGS. 2-7 a substrate 102 is processed as described above.At the end of this process, FIG. 7 illustrates a similar structure tothe structure illustrated in FIG. 12. In FIG. 7, the buried word line115 comprises metal layer 114 and second metal layer 116. In FIG. 12,the buried word line 115 comprises metal layer 114. Accordingly, asubstrate 102 processed through FIGS. 2-7 may subsequently be processedthrough FIGS. 12-14 as described above. Finally, as described above, asubstrate 102 processed to FIG. 14 may be further processed throughFIGS. 8-10 to form a memory device.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,”“upper” and the like, may be used herein for ease of description todescribe one element or feature's relationship to another element(s) orfeature(s) as illustrated in the figures. It will be understood that thespatially relative terms are intended to encompass differentorientations of the device in use or operation in addition to theorientation depicted in the figures. For example, if the device in thefigures is turned over, elements described as “below” or “beneath” otherelements or features would then be oriented “above” the other elementsor features. Thus, the exemplary term “below” may encompass both anorientation of above and below. The device may be otherwise oriented(rotated 90 degrees or at other orientations) and the spatially relativedescriptors used herein interpreted accordingly.

The use of the terms “a” and “an” and “the” and similar referents in thecontext of describing the materials and methods discussed herein(especially in the context of the following claims) are to be construedto cover both the singular and the plural, unless otherwise indicatedherein or clearly contradicted by context. Recitation of ranges ofvalues herein are merely intended to serve as a shorthand method ofreferring individually to each separate value falling within the range,unless otherwise indicated herein, and each separate value isincorporated into the specification as if it were individually recitedherein. All methods described herein can be performed in any suitableorder unless otherwise indicated herein or otherwise clearlycontradicted by context. The use of any and all examples, or exemplarylanguage (e.g., “such as”) provided herein, is intended merely to betterilluminate the materials and methods and does not pose a limitation onthe scope unless otherwise claimed. No language in the specificationshould be construed as indicating any non-claimed element as essentialto the practice of the disclosed materials and methods.

Reference throughout this specification to “one embodiment,” “certainembodiments,” “one or more embodiments” or “an embodiment” means that aparticular feature, structure, material, or characteristic described inconnection with the embodiment is included in at least one embodiment ofthe disclosure. Thus, the appearances of the phrases such as “in one ormore embodiments,” “in certain embodiments,” “in one embodiment” or “inan embodiment” in various places throughout this specification are notnecessarily referring to the same embodiment of the disclosure. In oneor more embodiments, the particular features, structures, materials, orcharacteristics are combined in any suitable manner.

Although the disclosure herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent disclosure. It will be apparent to those skilled in the art thatvarious modifications and variations can be made to the method andapparatus of the present disclosure without departing from the spiritand scope of the disclosure. Thus, it is intended that the presentdisclosure include modifications and variations that are within thescope of the appended claims and their equivalents.

What is claimed is:
 1. A method of testing a memory device, the methodcomprising: forming a thickness of a metal layer within a plurality oftrenches, each trench having a trench depth, the thickness at leastfilling the trench; recessing the metal layer to a predetermined depthto form a recessed metal layer; depositing a high density dielectriclayer on the recessed metal layer; performing a high temperature anneal;removing the high density dielectric layer; and evaluating the metallayer for voids.
 2. The method of claim 1, wherein forming the metallayer comprises: depositing a conformal gate oxide layer in theplurality of trenches; depositing a conformal work-function metal layeron the conformal gate oxide layer; and depositing the metal layer on theconformal work-function metal layer.
 3. The method of claim 1, whereinthe metal layer comprises Ru or Ir.
 4. The method of claim 1, whereinthe predetermined depth is in a range of 80 nm to 90 nm.
 5. The methodof claim 1, wherein the high density dielectric layer comprises siliconnitride or silicon carbonitride.
 6. The method of claim 1, wherein thehigh temperature anneal is performed at a temperature in a range ofabout 850° C. to about 950° C.
 7. The method of claim 1, wherein thehigh temperature anneal is performed for a period in a range of about 1minute to about 5 minutes.
 8. The method of claim 1, wherein the highdensity dielectric layer comprises silicon nitride and removing the highdensity dielectric layer comprises a hot phos etch process.
 9. Themethod of claim 1, wherein evaluating the metal layer for voidscomprises an e-beam metrology process.
 10. The method of claim 9,wherein the e-beam metrology process has an energy in a range of about10 keV to about 25 keV.
 11. The method of claim 1, wherein after thehigh temperature anneal, the metal layer contains substantially no seamsor voids.